Infection with human immunodeficiency virus (HIV) commonly results in neurologic disease termed the AIDS dementia complex (ADC). Neuronal loss and injury have been found in the HIV-infected brain, but the underlying mechanisms are poorly understood. The simian immunodeficiency virus (SIV) infected macaque is an excellent model for HIV infection, but neuronal loss has not been demonstrated. To determine whether neuronal damage occurs in the SIV-infected macaque we quantified the neuronal marker n-acetylaspartate (NAA) using proton magnetic resonance spectroscopy in brain extracts of control and SIV-infected macaques and correlated these findings with histologic analyses. We found reduced NAA in the SIV-infected animals compared to controls (2.94+1.37 versus 6.21+1.73 mols/g wet weight; p=0.004). A significant decrease in NAA was also found in SIV-infected animals sacrificed in the acute stages of infection. We conclude that SIV infection of rhesus macaques results in neuronal damage that is demonstrable soon after infection.